Method for combined coating and cold reduction of metal

ABSTRACT

METAL SHEET OR STRIP FORMED THROUGH A COLD MILL TO REDUCE IT TO SUBSTANTIALLY FINAL GAUGE IS COATED THROUGH CONTACT WITH THE MILL ROLLS, WITH A FLUID WHICH IS CAPABLE OF CROSS LINKING OR OF POLYMERISATION UNDER THE ACTION OF RADIATION OF AN ACCELERATED ELECTRON BEAM, X-RAYS OR GRAMMA RAYS OF PROVIDING A DEGREE OF LUBRICATION OF THE MILL ROLLS. THE COATED STRIP IS THEN SUBJECT TO RRADIATION, EITHER DIRECTLY AFTER COATING OR AFTER AN INTERMEDIATE STORAGE STEP INCLUDING FOR EXAMPLE COILING AND UNCOILING.

April 17, 1913 w JENKINS ET AL 3,128,147

METHOD FOR COMBINED COATING AND com) REDUCTION OF METAL Filed Sept. 18, 1970 Q 5 5 5 Q Ev m@ mi w United States Patent Oflice 3,728,147 Patented Apr. 17, 1973 3,728,147 METHOD FOR COMBINED COATING AND COLD REDUCTION OF METAL Walter Norman Jenkins and Terence Williams, Swansea, Wales, assignors to The British Iron and Steel Research Association, London, England Filed Sept. 18, 1970, Ser. No. 73,350 Claims priority, application Great Britain, Sept. 23, 1969, 46,796/69 Int. Cl. B44d 1/50 US. Cl. 117-93.31 16 Claims ABSTRACT OF THE DISCLOSURE Metal sheet or strip formed through a cold mill to reduce it to substantially final gauge is coated through contact with the mill rolls, with a fluid which is capable of cross linking or of polymerisation under the action of radiation of an accelerated electron beam, X-rays or gamma rays of providing a degree of lubrication of the mill rolls. The coated strip is then subject to radiation, either directly after coating or after an intermediate storage step including for example coiling and uncoiling.

This invention relates to the production of metal sheet or strip having a protective coating and is particularly concerned with the production of coated steel sheet or strip.

In the production of steel sheet or strip, hot band material, i.e. material produced by hot rolling is subsequently cold reduced in mill stands which exert considerable pressure upon the sheet being Worked.

For reasons of heat removal improving surface finish, lowering rolling pressure and, to preserve the cleanliness of the cold mill rolls, rolling oil is applied to the rolls and a film of this oil is consequently retained upon the surface of the reduced sheet or strip material.

In a number of production processes, the cold reduced material is subject to heat treatment eflective to modify the characteristics of the final product. The cold reduced material may for example be decarburised, it may be heat treated to relieve stress introduced during cold rolling or it may be heat treated to improve further the surface finish. Such heat treatment generally occurs at temperatures up to 700 C. and in this temperature range the residual oils is in general removed by evaporation.

It is becoming common practice, as a result inter alia of improved steel starting material, to dispense with final heat treatment and to utilise sheet material immediately after cold reduction. In this case, the rolling oil film must be otherwise removed in an independent cleaning process which both reduces the speed of the rolling procedure and increases the cost of the rolled product.

The present invention is based on the discovery that by suitable selection of fluid eflective to provide lubrication of cold mill rolls, the need to remove the residual fluid film by cleaning can be dispensed with.

According to one aspect of the present invention, a process for producing cold rolled metal sheet or strip having a protective coating, including subjecting to radiation of an accelerated electron beam X-rays or gamma rays, sheet or strip which has been coated through contact with the rolls, with a layer fluid capable of cross linking or polymerisation under the influence of the radiation and effective to provide a degree of roll lubrication.

By cross linking or polymerising the fluid, the radiation fully or partially hardens the coating to provide a protective layer on the sheet or strip. The invention thus not only dispenses with the need to clean the cold rolled material, but also provides it with a protective coating enabling the material to be used, for can making and the lilile :vhere a protective layer must in any event be prov1 e A suitable fluid may be selected from those commonly used to provide lubrication of cold mill rolls and known in the art as rolling oils or from any other fluid capable of cross linking or polymerisation under the influence of radiation. Examples of suitable fluids other than rolling oils are polymers such as polyethylene, liquid paralfin, natural oils and dioctyl sebacate.

The fluid may be applied to the mill rolls by any means well known in the art, for example, by spraying through suitably spaced apart nozzles adapted to provide overlapping spray areas at the rolls to ensure complete cover age.

In a preferred embodiment of the invention, a further coating of a material capable of cross linking or polymerisation is applied to the fluid coating acquired by the sheet or strip during cold rolling, and the composite coating is subjected to irradiation in vacuum by an accelerated electron beam, X-rays or gamma rays to cross link or polymerise both coatings and provide an improved protective layer.

In some cases it has proved difficult to apply the overlying coating upon the initial coating of fluid applied directly to the sheet or strip by the mill rolls. In this case, the initial coating may initially be partially or fully cured by exposure under vacuum to radiation of an accelerated electron beam, X-rays or gamma rays.

Preferably, the further coating of material is produced by vacuum deposition; however, the further layer may be produced by other techniques well known in the art, prior to curing by radiation.

An embodiment of the invention will now be particularly described by way of example with reference to the accompanying drawing which is a schematic side view of an apparatus to produce a protective coating upon continuous steel strip.

Referring to the drawing, steel strip produced by hot rolling and subsequently cold reduction is shown emerging at substantially final gauge 2 from the nip of end rolls 4. Applied to the rolls of the cold mill and particularly to the end rolls 4 is a fluid capable of cross linking or polymerisation under the action of radiation of an accelerated electron beam, X-rays or gamma rays, and of providing a degree of lubrication of the rolls. In the example, the fluid is applied to the rolls 4 by way of nozzles (not shown) which provide overlapping areas of spray at incidence upon the rolls to ensure complete coverage. However, any form of applying fluid to the rolls well known in the art may be used.

Strip 2, which acquires a coating of fluid by contact with the rolls 4, passed through an oven 6 effective to spread or/ and to fully or partially dry the coating. After spreading and/or drying the continuous strip passes through a vacuum chamber 8, the entrance and exit of which are closed by vacuum seals 10 and 12 respectively, each seal comprising a plurality of roller seals 14 each positioned in a vacuum chamber. The vacuum chamber 8 is provided with a plurality of electron guns 16 for irradiating the coated strip passing through the chamber.

After irradiation, which may alternatively be by X- rays or gamma rays the coated strip leaves the vacuum chamber 8 through the seal 12.

To further understand the invention, the following examples are given by way of illustration only.

EXAMPLE 1 Palm oil was applied to the rolls 4 to leave a residual coating upon the strip 2 which was spread to uniformity by passage through the oven 6. The dried residual coating was then cured by an electron beam from the guns 16 at an accelerated voltage of 10 kv. although voltages up to 15 kv. may be used. The beam current was adjusted to raise the temperature of the strip to about 200 C. to produce complete curing, which was established when the coating became completely insoluble in methyl ethyl ketone.

EXAMPLE 2 The strip with the cured coating provided by Example 1 was vacuum coated with an epoxy resin having an average molecular weight between 900 and 1400 giving a final coating thickness of about 3 microns. The composite coating was passed into a vacuum chamber substantially identical to chamber 8 and cured by an electron beam accelerated at 10 kv. and a current again effective to raise strip temperature to 200 C.

The composite coated strip was shown to have properties similar to an epoxy coating as currently used in the art to lacquer tin plate.

In an alternative example, the epoxy resin may be applied to the layer of palm oil or other rolling oil or fluid which has been only partly cured by passage through the irradiating chamber 8, for example by reducing the beam current from the electron guns 16. In some cases, the partial curing of the initial coating may be entirely dispensed with and the epoxy resin may be deposited, either under vacuum or at substantially atmospheric pressure, directly onto the initial coating. The composite coating again is then cured by irradiation in the manner described.

It will be appreciated that while the examples have been described with references to palm oil, any fiuid capable of cross linking or polymerisation under radiation may be used. Examples of such fluids are low molecular weight materials such as polyethylene which display suflicient lubricating quantities and provide an acceptable coating, as well as liquid paraffin, natural oils and dioctyl sebacate.

It will be appreciated that while cold reduced material coated with fluid is fed directly into a curing chamber alternative arrangements are within the scope of the invention. For example the coated strip emerging from the cold mill rolls FIG. 4 may be coiled for storage and subsequently uncoiled for the curing operation.

'What we claim is:

1. A process for producing cold rolled metal sheet material having a protective coating which comprises the steps of coating said sheet as it passes between the rolls of a reducing mill with a layer of fluid which provides roll lubrication while fluid and which is capable of cross-linking or polymerization under the influence of radiation selected from the group consisting of an accelerated electron beam, X-rays and gamma rays, and subjecting said sheet to such radiation after it has passed through said rolls.

2. A process as claimed in claim 1 wherein the fluid is applied directly to the mil rolls for transfer to the metal sheet or strip.

3. A process as claimed in claim 2 wherein the fluid is sprayed onto the rolls through spaced nozzles.

4. A process as claimed in any preceding claim wherein the fluid is a polymer.

5. A process as claimed in claim 4 wherein the fluid is polyethylene.

6. A process as claimed in claim 1 wherein the fluid is an oil.

7. A process as claimed in claim 6 wherein the fluid is liquid paraffin or a rolling oil normally used to provide lubrication of cold mill rolls.

8. A process as claimed in claim 7 wherein the rolling oil is palm oil.

9. A process as claimed in claim 1 wherein the fluid is dioctyl sebacate.

10. A process as claimed in claim 1 wherein the sheet or strip is heated to assist polymerisation or cross linking.

11. A process as claimed in claim 10 wherein the irradiating electron beam current is adjusted to control the heating of the sheet or strip.

12. A process as claimed in claim 1 wherein the initial layer is covered by an overlying layer of material capable of cross linking or polymerising by radiation of an accelerated electron beam, X-rays or gamma rays.

13. A process as claimed in claim 12 wherein the overlying layer is vacuum deposited.

14. A process as claimed in claim 12 wherein the initial layer of fluid is partly or fully cured by radiation before deposition of the overlying layer.

15. A process as claimed'in claim 1 wherein the sheet or strip is stored or coiled intermediate being coated with fluid at the cold mill rolls and irradiation.

16. A process as described in claim 1 wherein the sheet or strip is of steel.

References Cited UNITED STATES PATENTS 3,090,698 5/1963 Wilson 117-9331 3,110,413 11/1963 McKay et al. 220-64 3,287,264 11/1966 Topper 252-56 R 2,689,545 9/1954 Nelson l171 11 R RALPH S. KENDALL, Primary Examiner J. H. NEWSOME, Assistant Examiner U.S. Cl. X.R.

7242; ll7--l32 C; 252-ll, 56 S 

